1. Field of the Invention
The present invention relates to a display device utilizing a conductive transparent oxide layer as an electrode. Specifically, an object of the invention is to improve a light-emitting element in a luminescence property, to improve resistivity of an electrode, and to reduce power consumption of a display device by controlling a concentration of silicon or silicon oxide in the conductive layer.
2. Description of the Related Art
A light-emitting element formed by mainly sandwiching a material that emits electroluminescence (hereinafter referred to as “EL”) made from an organic compound between a pair of electrodes is drawn attention. This light-emitting element is an element that utilizes a phenomenon of emitting light when recombining a hole injected from one electrode and an electron injected from the other electrode and returns to a ground state.
That is, this kind of light-emitting element is formed so that organic compounds having different carrier transport properties between a pair of electrodes are laminated, a hole can be injected from one electrode, and an electron can be injected from the other electrode. Injection of a hole and an electron into the organic compound is assumed one index by a size of a work function (a minimum energy that is necessary for extracting one electron to just the outside from a surface of metal or a semiconductor) of a material that forms an electrode. It is preferable that an electrode on the side of injecting a hole has a high work function, and an electrode on the side of injecting an electron has a low work function.
Conventionally, indium tin oxide (ITO) of which work function is approximately 5 eV is used for an electrode on the side of injecting a hole, which is called an anode, and is in contact with an organic compound having a high hole transport property. In addition, an alkali metal such as Li, Na, or, Mg, alkaline earth metal, Al, Ag, In, or an alloy containing them with a low work function is used for an electrode on the side of injecting an electron, which is called cathode, and is in contact with a material having a high electron transport property (Reference 1: Japanese Patent Application Laid-Open No. 2000-268954).
In addition to a hole injection layer such as copper phthalocyanine (CuPc) or molybdenum oxide (MoOx), a hole transport layer such as 4,4′-bis-[N-(naphthyl)-N-phenyl-amino]biphenyl (α-NPD) which is an aromatic amine material, or an electron injection layer or an electron transport layer such as tris-8-quinolinolatoaluminum complex (Alq3), a light-emitting layer added with a guest material such as quinacridon into a light-emitting material such as Alq3 or rubrene, or a host material such as 4,4′-bis(N-carbazolyl)-biphenyl (CBP) or 2,2′,2″-(1,3,5-benzenetol-yl)-tris[1-phenyl-1H-benzimidazole] (TPB1) is known as an organic compound.
In order to improve a luminescence property of a light-emitting element, it is necessary to inject an electron and a hole efficiently from electrodes, to transport an injected electric charge efficiently to a light-emitting layer, to improve the recombining efficiency of the electron and the hole, and to improve luminous efficiency after recombining.
However, adequate luminance is not obtained in a conventional light-emitting element, that is, a light-emitting element having a structure in which an organic compound is sandwiched between an anode made from ITO or the like and a cathode made from MgAg, Al, and the like. In addition, power consumption is large and half-life time of luminescence is short in the conventional light-emitting element; therefore, there is a problem to be solved in respect of stability.